Serum Level of Anti-Nucleocapsid, but Not Anti-Spike Antibody, Is Associated with Improvement of Long COVID Symptoms.

BACKGROUND

Long COVID is a condition characterized by long-term sequelae persisting after the typical convalescence period of COVID-19. Previous reports have suggested the role of an unsatisfactory immune response and impaired viral clearance in the pathogenesis of long COVID syndrome. We focused on potential associations between post-vaccination changes of antibody titers and the severity of long COVID symptoms and factors influencing the state of remission observed in patients with long COVID after vaccination.

METHODS

The severity of long COVID symptoms and serum anti-SARS-CoV-2 spike (S-Ig) and nucleocapsid (NC-Ig) levels were assessed in 107 post-COVID subjects at two time points: at baseline, and 17-24 weeks later. Besides, vaccination status was also assessed. Symptoms were evaluated based on the Chalder fatigue scale (CFQ-11) and visual analogue scale (VAS).

RESULTS

Serum level of S-Ig and NC-Ig at baseline were significantly higher in the patients with non-severe fatigue than those with severe fatigue, and this difference remained significant at follow-up in the case of NC-Ig. NC-Ig level above median was as an independent predictor for complete remission at follow-up. The difference in NC-Ig levels in subgroup analyses (severe fatigue vs. non-severe fatigue; complete remission vs. incomplete remission or progression) was found to be significant only in patients who received vaccination.

CONCLUSIONS

The immune response against the SARS-CoV-2 nucleocapsid may play a more important role than the spike in the course of long-term COVID syndrome.